What are you calling the new chain? I consider the "new chain" to be the chain that adopts the hardforking protocol change even if a supermajority of witnesses back it. I imagine this new chain would give special treatment to vested exchanges and power down their stake. I don't think it would make any change to Sun's stake, which currently has no protocol-level restrictions on it.

The legacy / community chain would also have Sun's stake. It's possible the community could decide to destroy ninja-mined stake. This perhaps would be the right move if Sun creates his own hardfork. But I think it may not be necessary. Do nothing. Leave Sun's property alone. The protocol should really be distinct from disputes.